Inflammation is signaled by redness, swelling, heat and pain as a reaction of the body against injury or assault. A variety of chemicals have been implicated as chemical mediators of the inflammatory reaction, including histamine, kinins, prostaglandins, platelet-activating factors, leukotrienes, and, from nerve endings, substance P. Mediators of the acute inflammatory reaction Seem to play roles in one or more of increasing vascular permeability, attracting leukocytes, producing pain, local edema and necrosis.
A variety of physiologic responses occur from the biological events that constitute the inflammatory processes. For example, Pinckard et al. at Chapter 10 describe platelet-activating factors ("PAF") in the text Inflammation: Basic Principles and Clinical Correlates (Gallin et al., Eds., 1988). This family of structurally related compounds appears to promote a variety of physiologic actions that are directly or indirectly related to inflammatory reactions. The authors note that PAF has been implicated in the pathogenesis of human disease conditions such as septic shock and organ transplantation rejection.
Swelling is a characteristic inflammatory response of tissues to injury. Swelling is produced by leakage of water and solutes of the blood directly into the tissue matrix. The increased leakiness of blood vessels after injury may be due to direct damage of blood vessels or may occur after the release of substances such as histamine (inflammatory mediators) that open up gaps between endothelial cells that line the blood vessels. A mild degree of swelling (or edema) does not affect the functional integrity of injured tissues (except perhaps in the brain), but, in severe injuries, massive swelling distorts tissue architecture, impedes the delivery of oxygen to cells, and causes extensive fluid loss from the vascular compartment. Thus, a pharmacological agent capable of inhibiting the swelling process may have therapeutic value in the treatment of tissue injuries.
Inflammation is also involved in various chronic conditions, such as asthma, although it is not presently clear which inflammatory cells or which particular mediators are significantly involved in asthma. Persson, "The Role of Microvascular Permeability in, the Pathogenesis of Asthma", European Journal of Respiratory Diseases, Suppl. No. 144, Vol. 68, pp. 190-204 (1986), concludes that extravasated plasma protein is always present in the airway lumen of asthmatic subjects.
There are steroid and non-steroid anti-inflammatory drugs known to the art. U.S. Pat. No. 4,579,844, inventors Rovee et al., issued Apr. 1, 1986, discloses topically treating an inflammatory condition of the skin by use of the prostaglandin synthetase inhibitor concurrently with a corticosteroid. U.S. Pat. No. 4,404,198, inventor Kelley, issued Sep. 13, 1983, discloses the topical application of a composition including phenyl salicylate to treat inflammation. U.S. Pat. No. 3,980,778, inventors Ayer et al., issued Sep. 14, 1976, discloses asteroid for use in the topical, oral or parenteral treatment of skin and mucous membrane inflammations. Ibuprofen (a known anti-inflammatory agent) has been tested in connection with UV-B-induced inflammation, but was found to have limited usefulness in treating sunburn reaction and is only somewhat more effective than placebo for the relief of symptoms associated with UV-B-induced inflammation after high dose UV-B phototherapy for psoriasis. Stern et al., Arch. Derm., 121, pp. 508-512 (1985).
U.S. Pat. No. 4,801,612, inventor Wei, issued Jan. 31, 1989, discloses the use of inhibiting an inflammatory response in the skin or mucous membranes of a patient by administering corticotropin-releasing factor or its analogs.
The first corticotropin-releasing factor (CRF, also called CRH or corticoliberin) to be characterized was a 41-residue peptide isolated from ovine hypothalami by Vale et al. (1981). Subsequently, the sequence of human-CRF was deduced from cDNA studies and shown to be identical to rat-CRF. More recently, caprine, bovine, porcine, and white sucker fish CRF have been characterized. The CRF of hoofed animals show considerable differences from that of man, but the pig and fish sequences differ from the human/rat sequence by only two out of forty-one residues.
For some unknown reason, peptides with homologous structures to mammalian CRF are found in cells of certain frog skins and in the urophysis of fish. In fact, the structure of sauvagine, the 40 amino acid peptide isolated from the skins of Phyllomedusa frogs, was reported several years before Vale's description of ovine-CRF. The structure of sucker fish urotensin I was reported just months after the description of ovine-CRF and resulted from an independent line of inquiry by Lederis's group in Canada. Although sauvagine and urotensin I release adrenocorticotropin from the pituitary, the functions of these peptides in the tree-frog (Phyllomedusa species that live in arid regions of South America) and in the sucker fish remain unknown. Recently, it has been shown that the sucker fish has its own hypothalamic CRF which is very close in structure to h/rCRF. Thus, the sucker fish would not require urotensin I for neuroendocrine regulation because it already has CRF in its hypothalamus.
Rat corticotropin-releasing factor (hereinafter "CRF") is described in U.S. Pat. No. 4,489,163, inventors Rivier et al., issued Dec. 18, 1984.
U.S. Pat. No. 4,415,558, inventors Vale, Jr. et al., issued Nov. 15, 1983, describes the synthesis of sheep CRF, analogs, and isolation of the oCRF from ovine hypothalamic extracts. The synthetic oCRF was found to lower blood pressure.
The generally similar peptide, sauvagine, was described in Regulatory Peptides 2, 1-13 (1981). Sauvagine is reported to have biological activity in lowering blood pressure in mammals and stimulating the secretion of ACTH and .beta.-endorphin.
U.S. Pat. No. 4,528,189, inventors Lederis et al., issued Jul. 9, 1985, and U.S. Pat. No. 4,533,654, inventors Lederis et al., issued Aug. 6, 1985, describe white sucker and carp urotensin I, respectively, as stimulating ACTH and lowering blood pressure.
The other CRF-related peptide, white sucker fish urotensin I, has an amino acid sequence the same as the carp urotensin, except the amino acid at the 24 position is Isoleucine and the amino acid at the 27 position is Glutamic Acid.
Ling et al., BBRC, 122, pp. 1218-1224 (1984), disclose the structure of goat CRF, which is the same as that of sheep. Esch et al., BBRC, 122, pp. 899-905 (1984), disclose the structure of bovine CRF which differs from sheep and goat CRF only by one amino acid residue (number 33 which is asparagine rather than the number 33 serine of goat and sheep CRF). Porcine CRF has been isolated and characterized by Patthy et al., Proc. Natl. Acad. Sci., 82, pp. 8762-8766 (1985). Porcine CRF shares a common amino acid sequence (residues 1-39) with rat/human CRF and differs from these only in position 40 and 41. Residue 40 can be either asparagine or isoleucine and residue 41 is phenylalanine-amide.
Both ovine and human/rat CRF have been used in clinical studies on the endocrine function of the pituitary-adrenal axis. Usually, doses of 1 to 5 .mu.g/kg have been injected intravenously to elicit endogenous release of adrenocorticotropin and increases in plasma corticosteroids. Higher doses of 10 .mu.g/kg and 30 .mu.g/kg of ovine-CRF were used by Orth et al., "Effect of synthetic ovine corticotropin-releasing factor. Dose-response of plasma adrenocorticotropin and cortisol.", J. Clin. Invest., 71, pp. 587-595 (1983), in the initial assessment of this hormone in man. The non-endocrine effects of this hormone include symptoms such as flushing, shortness of breath and physical signs such as an increase in minute volume, tachycardia and possible hypotension. These parameters return to baseline levels within 30 minutes and were not considered to be clinically harmful. The relative safety of CRF peptides is illustrated by the fact that CRF has been evaluated in normal children (aged 6-15 years) at a dose of 1 .mu.g/kg administered as an intravenous bolus, as reported by J. L. Ross, et al., "Ovine corticotropin-releasing hormone stimulation test in normal children", J. Clin. Endocrinol. Metab., 62, pp. 390-392 (1986).
Traditionally, pharmacologists have searched for new drugs that act as specific antagonists of inflammatory mediators. For example, candidate drugs that act as antagonists of the inflammatory mediators platelet-activating factor, leukotrienes, and bradykinin have been described. Specific mediator antagonists, by design, work one-on-one against substances that promote inflammation, and the efficacy of a single antagonist may be limited if more than one mediator is released during tissue injury. By contrast, an agonist, a term introduced by Reuse to describe a chemical that activates biological events, would be more efficacious than an antagonist if it could suppress convergent inflammatory processes initiated by more than one mediator. The concept of drugs as anti-inflammatory agonists was discussed by Svensjo and Persson in 1985 who showed that clinically used asthma drugs such as the .beta..sub.2 -adrenergic agonist terbutaline and the xanthine drug theophylline acted on specific receptors in the microvasculature to shut off plasma protein leakage induced by the inflammatory mediators histamine and bradykinin.
However, it would be advantageous to have peptides shorter than either CRF, sauvagine or urotensin I that possess anti-inflammatory agonist activity and that are efficacious for reducing vascular leakage. For example, the costs of producing a peptide with seven to twelve amino acid residues would be much less than the costs of producing one that is forty or forty-one residues long because each residue must be added to the next residue in a step-wise fashion. Also, the possibilities of obtaining more selective biological actions or oral/topical activity from shorter peptides are potential advantages to be considered.